The present invention relates generally to a tracking means for a belt-type abrading machine, and more specifically to an endless belt tracking system which accommodates belt stretch and belt wear and thus extends the useful life of such devices.
Belt-type abrading machines are known and used in the art for treatment of a variety of materials including wood as well as metals. Both grinding and finishing operations may be undertaken with either wood or metals. The abrasive belts, as is appreciated, are subject to substantial forces during abrading operations, and as such become stretched across the lateral extent thereof. When the stretch is uniform throughout the width of the belt, there is no adverse affect upon the ability of the belt to track, however such uniform stretch does not normally occur in practice. Non-uniform stretching results in the formation of anomalous belt configurations wherein the belts become conical rather than remaining cylindrical. Tracking becomes more difficult with abrasive belts having such anomalous configurations.
In the belt-type abrading machines in current use, two types of sensing and tracking systems are employed, the first being position sensing, the second being force-sensing. In position sensing operations, the belt remains in a substantially fixed axial or lateral disposition, subject to repositioning whenever the belt moves laterally outwardly of predetermined limit positions. In force-sensing, means are provided to cause the belt to respond to forces about the center point, with such sensing normally being desired to both extend the useful life of the belt and to provide more uniform wear across the surface of the abrasive belt. The tracking system of the present invention is primarily applicable to position sensing.
In the past, a variety of sensing systems have been developed and utilized, with one typical belt position sensor being disclosed and described in U.S. Pat. No. 3,971,166, as well as in U.S. Pat. No. 3,504,458. A control system for belt tracking is also disclosed in U.S. Pat. No. 3,118,314. In each of these systems, the endless belt is maintained within a predetermined path by selectively tilting or rocking the axis of a tensioning and tracking roll, with various means being applied to accomplish the tilting.
In each of these prior art systems, means are provided for angular adjustment of the tracking roll, with the Rutt Pat. No. 3,504,458 illustrating a force tracking system for accommodating angular adjustment or rocking of a tracking roll when a certain predetermined limit position has been reached. The tracking system of the present invention differs from that of U.S. Pat. No. 3,504,458 in that a generally continuous angular or arcuate adjustment and control of the tracking roll, with primary and secondary tracking drivers being employed, the primary driver being responsive to means detecting the immediate position of the belt and with the secondary driver being responsive to the integral of time that is required for the primary driver to adjustably drive the belt in either lateral direction. The time integration of the system may be readily accomplished by interposing a time-delay between the actuation of the primary belt tracking driver and the actuation of the secondary belt tracking driver and time-delay relays may be employed for this purpose.